Collapsible form jig



y 1965 c. FASSNACHT ETAL 3,184,210

COLLAPSIBLE FORM J I G 3 Sheets-Sheet 1 Filed June 25, 1962 w mm m M m MNE/A Wmmu 50mm BY May 18, 1965 c. FASSNACHT ETAL 3,134,210

GOLLAPSIBLE FORM JIG Filed June 25, 1962 3 Sheets-Sheet 2 INVENTORY6644,9451 Pass/v4 cw! y 1965 c. FASSNACHT ETAL 3,184,210

COLLAPSIBLE FORM J IG- 5 Sheets-Sheet 3 Filed June 25, 1962 0am504154854, $51849; iar/51v ,4 7 rum z 71' United States Patent 3,184,210r COLLAPSIBLE FORM JIG Charles Fassnacht, Philadelphia, and Neil WorrallBurwell, Southampton, Pa., assiwors to I-T-E Qircuit Breaker Company,Philadelphia, Pa., a corporation of Pennsylvania Filed June 25, 1962,Ser. No. 204,935 1 Claim. (Cl. 249-53) Our invention relates to theconstruction and contour checking of antennae structures and moreparticularly to the use of an inflatable pattern to form a contouredsurface adaptable for casting an antenna reflector (or r-adome), andchecking the contour of a previously formed antenna structure.

The mobility requirements of many electronic communications and radarsystems necessitates an antenna system that may readily be transportedand assembled at a designated installation site. Our invention increasesthe mobility capabilities of such systems by providing a truly tacticalantenna system in which the antenna reflector or radome is supplied as acompact kit of basically raw material and necessary tooling for on-sitefabrication.

It has been the practice of the prior art to fabricate the antennareflector and radome structures of such mobile antenna systems in thefactory. The reflector is then shipped to the installation site as aunit, or as a number of interlocking sections. Such prior art antennareflector structures may typically be formed of a plurality ofmechanical frame members and sectorial reflector sections, as set forthin our copending US. Patent application Serial No. 197,477, filed May24, 1962, entitled Antenna Transportable System, and assigned to theassignee of the instant invention.

Another method presently being practiced is to factory cast the antennastructure, and ship it as a unit to the site. When such structures arequite large, it has been the practice to cut the antenna into segments,which segments may then be assembled at the installation site to formthe overall antenna structure. Such prior art methods suffer from thedisadvantages of requiring large volumes to be transported, shipped, andstored at the installation site, thereby limiting their practicality astrue tactical equipment.

As an aspect of our invention, a collapsible pattern is used, which maybe inflated by the introduction of air to form an accurately contouredmold surface of a reflector surface. Such a bag-like mold pattern isfirst inflated to a sufiicient pressure to withstand the weight ofcasting material which is to be applied thereto to form the basic castreflector surface. A casting material, such as foamable polyurethane, isthen sprayed on the contoured surface of the reflector to the depthrequired for rigidity and strength. After curing, the inflatable patternis released, resulting in a cast reflector surface which is asubstantial duplicate of the image surface of the inflatable mold. Aconductive reflecting surface is then applied to the cast reflector, inan appropriate manner; such as by bonding a mesh screen, flame sprayingaluminum, or bonding a metal foil.

It is thus seen that our invention provides an improved apparatus formanufacturing a cast reflector, particularly adaptable for mobileantenna systems, permitting actual fabrication of the antenna at aremote installation site.

In a further aspect of our invention the above described collapsiblemold pattern is used as a jig to check the contour of a previouslyformed reflector surface. When it is desired to field-site check thecontour of a particular antenna reflector, the bag is pressurizedsufliciently to form the prescribed contour. The bag is then placed inan aligned position with respect to the antenna reflector and accuratefeeler gages may be utilized to of the radome structure.

3,l84,2lfl Patented May 18, 1965 check deviations in contour of theantenna reflector from the collapsible contour jig. The prior artmethods of contour checking typically include structural templates ofmetal, wood or plastic. Our method of contour checking eliminates theprior art utilization of such large and heavy structural forms and theiraccompanying tedious set-up and alignment procedures. The collapsiblebag of our invention may advantageously be rolled into a smalllightweight package for storing and shipping when not in use.

In still a further aspect of our invention the collapsible formedpattern may be utilized to construct a field site cast radome.Typically, a bag having a substantially spherical surface is firstinflated, in the manner set forth above, to form the radome contour. Thebag is then spray coated with a cast material, such as foamablepolyurethane, to a suflicient depth for strength and rigidity The spraycoating of the bag with the cast material may be performed on either theinternal or external surface of the bag; the former preferably permitsradome fabrication in a controlled environment and is especiallyadvantageous under inclement environmental conditions. Should the innerportion of the spherical bag be sprayed to form the radome, the bag ispreferably formed of a number of segments attached together to permitremoval after curing of the radome structure.

It is thus seen that the basic concept of our invention resides in theuse of an inflatable pattern to permit the fabrication and checking ofantenna reflectors or radomes at an installation site. The actualformation of the antenna structure at the remote installation sitegreatly enhances the mobility requirements of the resultant antennasystems.

it is accordingly a primary object of this invention to utilize acollapsible pattern to form a cast antenna structure.

A further object of this invention is to utilize an air inflatablepre-formed bag-like pattern as a contoured mold surface to form apolyurethane cast antenna reflector.

An additional object of this invention is to provide a field siteantenna reflector or radome kit comprising an inflatable mold patternand the basic materials utilized in the construction of the resultantantenna structure.

Another object of this invention is to provide a collapsible antennastructure pattern which comprises a pre-shaped bag constructed to beinflated to form a prescribed antenna structure contoured surface andadapted to provide a mold surface for the casting of an antennareflector.

Still an additional object of this invention is to provide a collapsiblebag-like radome pattern which may used to fabricate a foam-castpolyurethane radome at a remote installation site.

Still another object of this invention is to fabricate a quantity ofaccurately formed foamable polyurethane reflector surfaces by the use ofan inflatable pattern as a field site tool to form a mold surface.

Yet a further object of this invention is to provide an inflatableantenna pattern, including depth indicating means of varying lengthindications, to provide a tapered cast antenna structure.

These as well as other objects of our invention will readily becomeapparent after reading the following descriptions of the accompanyingdrawings in which:

FIGURE 1 is a perspective view of an antenna structure patternconstructed in accordance with the teachings of our invention, shownfully inflated.

FIGURE 2 is a perspective view of the reflector pattern of FIGURE 1deflated and rolled up to indicate its compact shipping and storagerequirements.

FIGURE 3 is a side elevation of the inflated antenna pattern of FIGURE 1being used to forma cast antenna reflector.

FIGURE 4 is a cross section along line 4-4 of FIG URE 3 and looking inthe direction of 'the arrows which typically illustrates the manner inwhich the depth indicating posts may be secured to the antenna reflectorpattern. FIGURE 5 is a perspective view, partially cut away, of anantenna reflector manufactured in accordance with the teachings of ourinvention. a

FIGURE 6 typically illustrates the incorporation of an antenna reflectormanufactured in accordance with the teachings of our invention in amobile antenna system.

FIGURE 7 depicts the utilization of the inflatable reflector pattern ofour invention as a contour-checking jig.

FIGURES 8 and 9 illustrate the use of an inflatable mold pattern of ourinvention to form an antenna ra-' dome, showing the forming of theradome structure on the external and internal surface of the inflatablepattern respectively. 7

FIGURE 1 shows in perspective the collapsible mold pattern of ourinvention in the fully inflated position. The pattern is formed of abag-like enclosure 10 constructed of a flexible, but non-elastic,material such as rubberized canvas or nylon reinforced plastic. Theupper surface 11 of bag-like member 10 is pro-shaped to form aappropriate graduations.

. 4' Depth indicating posts 22 are preferably secured to surface '11in'a manner which facilitates the removal of the cast reflector 4i)containing such posts from pattern 10. FIGURE 4 shows one suchconnection of height indicating posts 22 to surfacell in which moldingsurface 11 contains a number of projections 23 appropriately placedanddimensioned to receive posts 22 Projections 23 arepreferably formedof the same material as inflatable pattern 10 and are permanentlyaffixed thereto. Depth indicating posts 22 contain a hollowed portionconstructed to slip-fit over projection 23. Height indicator 22 maytypically be a thin-Walled aluminum tube cut to the desired height'offoam above surface 11, or having Projectionfl23 is of ,suflicient heightto support the requisite length of tube 22 in the manner-shown in FIGURE4.

. After inflating of pattern 10 tothe proper pressure, and

the securing of depth indicating posts 22 and mounting i posts 24,antenna structure 11 is then sprayed with a 1 space-saving iseffected'by shipping material 20 in its raw mold surface for the antennastructure to be cast; illus- V,

state to the site, where'it is foamed to form the reflector 40. Castingmaterial 20 is preferably a polyurethane foam prepared by addingasurfactant, a bodying agent such as a colloidal silica, e.g., that ismarketed under the trade designation Cab-o-sil, and a fluorinatedhydrocarbon Pressure mean 15 is; i

stand the weight of casting material which is to be applied I V to formthe reflector structure.

FIGURE 2 illustrates the manner in which the deflated pattern 10 may berolled up to form an extremely compact package, thereby facilitatingpacking for shipping and storage at the installation site.

Reference is now made to FIGURE. 3, which'illustrates the inflatablepattern 10 being utilized to form an antenna reflector in accordancewith the teachings of our invention. Pattern 10 is inflated to asufiicient pressure to withstand the weight of the casting material 20applied thereto without distorting reflector contoured surface 11.Inflated pattern 10 is positioned on a suitable support 30, which maytypically be the ground plane. To facilitate the removal of mold 10after curing of the cast reflector, a releasing agent 21 is preferablyapplied to molding surface 11 prior to the'introduction of the castingmaterial, 20. The releasing compound 21 is preferably non-reactive witheither casting material 20 or the material comprising pattern 10, andwhen polyurethane materials are used for casting may typically beasilicon grease. Prior to the introduction of casting material 20 to thesurface 11 of mold 10 a plurality of depth indicating means, such asposts 22, are attached to surface 11. Each of the posts 22 areappropriately marked to indicate the desired depth of casting materialat their particular location to yield the requisite cast antennareflector (FIGURE 5), having sufficient rigidity and structuralstrength. The posts 22 at the extreme peripheral region are shownextended somewhat to provide a reinforced ring of casting materialcapable of withstanding the high tension loading about thiscircumferential region. Structural mounting posts 24 are also providedto be incorporated within cast reflector 40. These posts are constructedto facilitate blowing agent, e.g., a Freon,.to the casting resin. Theheat produced by the-exothermic reaction of these materials volatilizestheblowing agent, whic h'produces a cellular structure-in the resultantpolymerized material. These raw materials may be internally mixed byeither a static or rotary mixer at thesite, or mixed external to thespray gun and then applied to surface 11. The mixing and sprayingequipment utilized to form foamable poly urethane from the, rawmaterials shipped to the site is preferably a portable device; one suchdevice being the model DPSG-A spray gun and metering unit, manufacturedby the Decker Industries Division of Stuart Marine, Stuart, Florida.After spraying to a sufiicient depth, material 20 is permitted to cure.The foamable polyurethane casting material'20utilized preferably'permitsfor such FIGURE 5.

Cast antenna 40 has an internally concave parabolic surface 41corresponding to the image contour of convex mold surface 11. Areflecting surface 42 having the requisite electrical characteristics toimpinging radiation of the particular antenna requirement is thenapplied to surface 41. Surface 42 is shown as a mesh screening bonded tosurface 41, but may alternativel be flame sprayed aluminum for a bondedfoil. Reflecting surface 42 is shown coated with a protective surface 43for environmental protection. Surface 43 may be paint, varnish, or thesame polyurethane material 20 used to cast the reflector structure.

' Reference is nowmade; to FIGURE 6, whichillustrates 'a typical antennasystem utilizing the antenna reflector 40 constructed ,in'accordancewith the teachings of our invention. Mounting' ring .25 is connected inan appropriate manner to the upper portion of elevating structure 51.Base pad 52 connected to the lower portion of structure 51 includes aball andsocket joint, permitting rotation about that point to facilitatethe lowering and raising of'elevation member 51. Guy lines 53, 54anchored at 55, 56 respectively stabilize elevated member 51. Feed 60 isillustratively shown'as a dual polarized feed with wave guides 61 and 62connected to reflector 40 in an appropriate manner. It is naturallyunderstood that feed 60 is shown for illustrative purposes only, andvarious other types of feeds presently known in the art may be used inconjunction with the particular reflector 42 and system requirements.

FIGURE 7 illustrates the manner in which inflatable pattern may be usedas a jig to check the contours of a previously formed antenna reflector70. Reflector 70 may be of any presently known construction includingthat of above-described reflector 40. Reflector 70 is illustrativelyshown mounted to antenna system 50. Elevating structure 51 is lowered bythe use of cables 53, 54 in conjunction with gin pole 58 to pivot aboutbase pad 52. Antenna 70 is then maintained in an aligned position withrespect to reflector pattern 10. Height indicators 71 are then used tocheck for uniform distance between the concave surface 72 of antenna 70and the convex pattern surface 11. Depth indicator 71 may be uniformheight posts secured to surface 11 in the same manner as post 22 (shownin FIGURE 4). Alternatively, height indicator 71 may be a Verniercaliper continually positioned about the mating parabolic surfaces 11,72 to check for uniformity of distance and hence accuracy of contour.Where inflatable mold 10 is used to check the contour of an opened meshsurface formed of metal framing, such a mold may be directly positionedwithin the antenna reflector and in contact with its concave surface.Feeler gauges may then be inserted from the rear of the antenna toascertain portions of the surface 71 which do not mate with thecontoured pattern surface 11. Hence, it is seen that the use ofaccurately pre-formed surface 11 of pattern 10 avoids the prior art needof rather large and intricately assembled heavy structural templates forfield site antenna contour checking.

FIGURES 8 and 9 illustrate another aspect of our invention wherein theinflatable mold 10' is used as a pattern for the casting of a radomestructure 80, in the manner similar to that discussed above for thecasting of cast reflector 40. Inflatable mold 10' is pre-formed to asubstantially spherical configuration having a principal diameter whichmay typically be to 80 feet. Mold 10' is pressurized sufliciently towithstand the weight of casting material which will subsequently beapplied thereto to form the radome structure 80. A releasing compound 81is preferably applied to the foam receiving convex surface 11' of mold10'. In addition, depth indicating means similar to post 22 of FIGURE 3(not shown) may be added to indicate the thickness of foamable materialthat has been applied. The foamable material applied to radome pattern10 is preferably of the same type of foamable polyurethane utilized inthe construction of antenna reflector 40. After being sprayed to theproper thickness to form a radome structure 80, of proper structuralstrength and rigidity, the cast structure is cured, after which bag 10may be removed.

FIGURE 9 illustrates a modification of the method utilized to formradome 80, wherein the inner concave surface 11" of inflatable radomepattern 10 is used as the mold surface. This method is particularlyadvantageous where it is desirable to form a radome structure in aninclement environment, such as the Arctic. By applying the castingmaterial within the volume enclosed by the radome, a controlledenvironment conducive to polyurethane spraying may be provided. Tofacilitate removal of antenna pattern 10" from the embodiment shown inFIGURE 9, pattern 10" is preferabl constructed of a number of individualsegments joined in an appropriate manner, such as hooks 82 and eyelets83. After the curing of radome structure 80, the necessary doorways andwindows may be cut in the polyurethane cast structure.

Thus it is seen that our invention permits the utilization in the fieldof basic raw materials to form an antenna structure, typically areflector or radome. An inflatable pattern having the requisite contoursis used, and such an inflatable pattern is preferably adaptable to alsobe used for checking the contours of a reflector surface. Although ourinvention may be used for forming both relatively small and largereflecting surfaces, it would have its greatest value in the formationof larger reflectors, wherein factory fabrication and shipment is lessfeasible. Typically, it may be used to form a reflector up to 30' indiameter, with considerable accuracy and permitting appreciable costsavings over the methods presently being used. Specifically, we haveillustrated our invention utilizing a particularly contoured reflectorsurface and radome, and a particular composition of casting material. Itis naturally understood that the basic concept of our invention may bepracticed to construct various other antenna structures in the field andwith the use of various other casting material compositions. Thus, weprefer not to be bound by the specific disclosure herein, but only bythe appended claim.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

A collapsible antenna structure pattern comprising: a pre-shaped bag;said bag constructed to be inflated to form a prescribed antennastructure contoured surface; said surface adapted to provide a convexmold surface defining a paraboloid of revolution for the casting of anantenna reflector; said bag constructed of a flexible, nonelasticmaterial, and air pressurized to accurately form said prescribed antennastructure contoured surface; said bag being sufliciently pressurized forsaid mold surface to support a reflector casting; a plurality ofupstanding, substantially uniform height projections extending away fromsaid convex mold surface; a plurality of depth indicating meansindividually seated on said projections and extending away from theantenna reflector surface to be cast, to indicate reflector castingthickness; said depth indicating means comprising posts of varyinglength indications to provide a tapered antenna structure; thecooperative seating of said depth indicating means and projectionsconstructed to permit ready release, whereby a concave parabolic antennastructure molded to proper tapered distance may be readily removed.

References Cited by the Examiner UNITED STATES PATENTS 1,733,034 10/29Tufenkjian. 2,022,510 5/3 5 Rosenblatt. 2,335,300 11/43 Netf 25-131.52,388,701 11/45 Neff. 2,689,304 9/54 Lawrence 3439l2 XR 2,753,276 7/56Brockhagen et al. 2,779,689 1/57 Reis 1848 XR 2,816,323 12/57 Runger.2,948,896 8/60 Hart 343912 XR 2,969,544 1/61 Di Marco et al. 343-9123,076,226 2/63 Borton et al.

FOREIGN PATENTS 211,170 6/09 Germany.

OTHER REFERENCES Aviation Week, Radically New Radar Antenna Infiates,Oct. 22, 1956, pp. 94, 95, 97 and 98.

Science News Letter, Sun-Proof Igloo, vol. 77, No. 1, Jan. 2, 1960, p.7.

WILLIAM J. STEPHENSON, Primary Examiner.

MORRIS LIEEMAN, ALEXANDER H. BRODMER- KEL, MICHAEL V. BRINDISI,Examiners.

